Air fryer displays E4 and will not start a cooking cycle.

Safety: Unplug the Ultrean air fryer and let it cool for at least 30 minutes. Internal components may be very hot.

Steps to check E4:

• Basic reset: After a full cool-down, plug the unit back in and try a low-temperature setting (e.g., 300°F/150°C). If E4 appears immediately, proceed to internal checks.
• Clean interior: Remove basket and pan. Thoroughly clean grease and carbon buildup from the basket, pan, and inner cavity walls. Pay attention to the area around the heating element and fan guard.
• Access heater circuit: Turn the unit upside down and remove the bottom cover. Trace the wires from the heating element; you should find a small thermal fuse or thermostat in series.
• Check thermal fuse/thermostat: With the unit unplugged, use a multimeter to test continuity across the thermal fuse and any inline thermostat. An open reading indicates a blown or tripped device.
• Inspect for heat damage: Look for discolored, brittle, or melted insulation around the heater and thermal fuse. This suggests chronic overheating.
• Replace components: If the thermal fuse is open, replace it with an identical temperature and current rating, using high-temperature wiring. If there is a manual-reset thermostat (small disc with a button), press the reset if accessible; if it will not reset or is open, replace it.
• Control board check: If all thermal devices test good but E4 persists, the main control board may be faulty and should be replaced.

Important: Never bypass a thermal fuse or thermostat; doing so removes critical safety protection and can cause fire.